A process for manufacturing a semiconductor device includes performing a liquid processing by supplying a processing liquid to an upwardly facing front surface of a substrate, such as a semiconductor wafer, while rotating the substrate around a perpendicular axis in a horizontal position. In some cases, simultaneously with performing the liquid processing on the front surface of the substrate that faces upward, the liquid processing is also performed on the rear surface of the substrate that faces downward by supplying the processing liquid to the rear surface of the substrate. Further, in some cases, when the liquid processing is performed on the front surface of the substrate, a gas such as, for example, nitrogen gas, may be supplied to the rear surface of the substrate in order to suppress the processing liquid supplied to the front surface of the substrate from flowing to the rear surface side, to suppress contaminants from being attached to the rear surface of the substrate, or to reduce an oxygen concentration in a space formed at the rear surface side of the substrate.
When the gas is supplied to the rear surface of the substrate, it is desired that the space formed below the substrate is narrow in order to achieve the above-described purposes with a small flow rate of the gas. Meanwhile, it is not desired that the area of the space below the substrate when the processing liquid is supplied to the rear surface of the substrate is the same as that when the gas is supplied to the rear surface of the substrate. In this case, it is desired that the space formed below the substrate is relatively wide such that the processing liquid supplied to the central portion of the rear surface of the substrate smoothly flows to the peripheral edge of the substrate via the rear surface of the substrate.
For a user of a substrate processing system, it is desired that a single substrate processing unit is commonly available for a plurality of kinds of processings from the viewpoints of both apparatus costs and foot print reduction.
The above-described demand may be partially responded by providing a disc-shaped member, which is liftable and rotates together with a substrate holding member, below a substrate so as to adjust a gap between the substrate and the disc-shaped member as disclosed in Japanese Laid-Open Patent Publication No. 2002-270563. However, when a lift driving mechanism configured to lift the disc-shaped member is mounted in the substrate holding member that is a rotational body, the structure of the substrate processing unit becomes complicated, and particle generation sources are increased. The particle generation sources also easily cause the weight increase and rotational unbalance of rotation bodies and rotational unbalance.